Urea-formaldehyde resin compositions are employed in large quantities for diverse industrial purposes. Such resin compositions typically are prepared by condensing 1.5 - 2.0 mols of formaldehyde with 1 mol of urea i an aqueous medium under weakly acidic or mildly alkaline conditions. After the condensation has been carried out, the ph is adjusted to about 7 or slightly higher, and water is evaporated from the resin solution to increase the solids content of the resin compositions to the order of 60 - 75% by weight.
Urea-formaldehyde resin compositions of the type described above tend to polymerize when stored at ambient temperature, the rate of polymerization increasing with temperature. The polymerization of such resins is noted by an increase in the viscosity of the resin compositions. Accordingly, careful control of inventories of such resin compositions is required so that the resins do not polymerize to the extent that they cannot thereafter be used for their intended purpose.
Considerable studies have been made of methods for preparing such aqueous resin compositions which are free of the undesirable tendency to polymerize at ambient temperature. While minor reductions in the tendency to polymerize in storage can be obtained by careful manufacturing processes, virtually all aqueous urea-formaldehyde resin compositions nevertheless polymerize during storage.